Diamond Nitrogen Vacancies (DNVs) can be used to measure very small changes in magnetic fields when properly excited by radio frequency (RF) and optical fields. Continuous wave (CW) excitation schemes require a delicate balance between the RF energy used to excite the DNVs and the laser power required to reset the diamond quantum state. This balance constrains the magnetometer sample bandwidth and sensitivity. Traditional CW laser/CW RF excitation limits the bandwidth of the sensor to respond to changing RF and associated intensity levels, particularly for vector applications (e.g., magnetometry or communication) involving excitation of nitrogen vacancies (NVs) across multiple diamond lattice vectors and resonance states.
Traditional DNV excitation schemes focus on pure CW excitation or pure pulsed excitation, where “pure” excitation indicates that both the laser/optical and the RF excitation are both either pulsed or CW. Current methods to increase magnetometer bandwidth (i.e. rate at which the magnetometer records data) in pure CW excitation schemes call for increasing laser power and RF power. However, a balance is required between the RF energy required to excite the DNV system and the laser power required to restore the diamond quantum state. For example, while higher RF power may increase intensity contrast, it also requires a longer polarization time to restore the diamond quantum state. Moreover, very high laser power systems are inefficient for functioning as low C-SWAP (cost, size, weight, and power) sensors.
Pure pulsed excitation schemes also prove to be inferior to continuous laser/pulsed RF excitation schemes if the timing jitter of the laser excitation after RF excitation is not sufficiently controlled or if the laser excitation ramp-up is not sufficiently consistent. Thus, laser pulsing in a pure pulsed excitation scheme may create a more dynamic thermal equilibrium than continuous laser excitation which can introduce additional noise into system measurements.
Moreover, for high-powered pulsed laser excitation, usual control methods involve acousto-optic modulators (AOM), which introduce additional vibration risks into sensor design, generally require large moment arms for the laser excitation path, and inherently sweep the laser onto the diamond-producing variations in the onset of laser excitation across the diamond (and in the thermal state of the NV across the diamond). The longer moment arm limits the ability to produce a low C-SWAP sensor.
A fundamental challenge for both pulsed and CW common excitation schemes is the time imbalance of dimming (measurement contrast due to non-fluorescent inter-system crossing of [NV−] for resonant RF frequencies) versus brightening (re-polarization of [NV−] quantum states) of the excited diamond. Brightening is often in excess of 100 times slower a process than dimming. For traditional pure CW excitation schemes, either the magnetometer bandwidth is limited by laser power or the sensitivity is limited by the RF power generated about the diamond.
A need exists for improved technology, including magnetic detection systems, and more particularly, for a magnetic detection system with pulsed RF methods for optimization of CW optical measurements.